1. Field of the Invention
This invention relates to liquid crystal light valve (LCLV) projectors, in general, and more particularly, to such projectors which provide color projection.
While the present invention is described with reference to particular applications, it is to be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings of this invention will recognize additional applications within the scope thereof.
2. Description of the Prior Art
The development of the liquid crystal light valve (LCLV) has opened the door to substantial progress in the state of the art of high quality large screen projectors. In the past, these projectors have been monochromatic or have used separate light valves for separate colors. The LCLV is a thin film, multilayer structure comprising a liquid crystal layer, a dielectric mirror, a light blocking layer, and a photoresponsive layer sandwiched between two transparent electrodes. A polarized projection beam is directed through the liquid crystal layer to the dielectric mirror. An input image of low intensity light, such as that generated by a cathode ray tube (CRT), is applied to the photoresponsive layer thereby switching the electric field across the electrodes from the photoresponsive layer onto the liquid crystal layer to activate the liquid crystal. Linearly polarized projection light passing through the liquid crystal layer and reflecting from the dielectric mirror is polarization-modulated in accordance with the information incident on the photoconductor. Therefore, if a complex distribution of light, for example a high resolution input image, is focused onto the photoconductor surface, the device converts that image into a replica which can be projected with magnification to produce a high brightness image on a viewing screen. U.S. Pat. No. 4,019,807 issued to D. D. Boswell et al. on Apr. 26, 1977 discloses such a high performance reflective mode liquid crystal light valve.
A graphics display projector using a liquid crystal light valve of the above-type is described in an article entitled "Application of the Liquid Valve to a Large Screen Graphics Display," published in the 1979 Society for Information Display (SID), International Symposium, Digest of Technical Papers, May 1979, pp. 22-23. This display system, a type with which the present invention is particularly but not exclusively concerned, projects a large scale image having yellow-wite characters on a dark blue background. The system includes a CRT which provides input imagery; projection optics which provides the bright collimated output beam and necessary light polarization; and the LCLV which interfaces the input and output functions.
The system uses a powerful light source such as a Xenon arc lamp to illuminate the LCLV through collimating and polarizing optics. Light emitted from the Xenon arc lamp is transmitted to a polarizing prism where it is separated into "S" and "P" components. The "P" component passes through the prism while the "S" component is reflected toward the LCLV. Information displayed by the cathode ray tube is transferred by fiber optics to one side of the LCLV where it activates the light valve to change the polarization of a portion of the state from "S" to "P". The light is then transmitted through the prism and imaged on a screen by the projection lens. In this capacity, the prism effectively functions as an analyzer, converting modulations of polarization to modulations of brightness or intensity.
The quality of the projected image is a function of its brightness, resolution, and contrast, as described in co-pending U.S. patent application of W. P. Bleha, Ser. No. 103,683, filed Dec. 14, 1979, entitled METHOD AND APPARATUS FOR ENHANCEMENT OF IMAGES DISPLAYED WITH A LIQUID CRYSTAL LIGHT VALVE (now U.S. Pat. No. 4,343,535) and assigned to the common assignee. This application describes techniques for reducing the irregularities and inhomogeneities in the polarizing prism and light valve.
Reference is also made to the co-pending U.S. patent application entitled POLARIZER-ANALYZER FOR LIQUID CRYSTAL LIGHT VALVE PROJECTORS, by R. S. Gagnon, bearing Ser. No. 297,904, filed on Aug. 31, 1981 and assigned to the common assignee. This application describes a unique polarizer element used in a monochromatic projector system using an LCLV.